Neutralization process



Unite States Patent 2,967,180 NEUTRALIZATION PROCESS Samuel C. Farrington, Hohokus, N.J., assignor to Lever Brothers Company, New York, N.Y., a corporation of Maine No Drawing. Filed Oct. 12, 1959, Ser. No. 845,652

8 Claims. (Cl. 260-400) This invention is concerned with a novel process for the neutralization of acidic impurities in the fatty acid esters of sodium isethionate. More particularly, it is concerned with the neutralization of acidic impurities, especially hydrogen chloride, by treating the impure material with soap.

The present application is a continuation-in-part of copending application, Serial No. 710,617,filed January 23, 1958, by Samuel C. Farrington,

Fatty acidesters of sodium isethionate which are the subject of the present invention are prepared by the reaction of a fatty acid acyl chloride with sodium isethionate according to the equation wherein R may be any aliphatic hydrocarbon radical. As can be seen from the above equation, this reaction results in the formation of hydrogen chloride, some of which remains to contaminate the fatty acid isethionate esters. Furthermore, since the preparation of the acyl chloride used as a reactant above is usually carried out by a reaction between the fatty acid and phosphorous trichloride, other impurities, for the most part acidic phosphorous containing substantances, are present in the acyl chloride and remain in the fatty acid isethionate ester after the reaction. These impurities must be neutralized to make the substance suitable for use in detergent compositions.

The conventional method for neutralizing such impurities has been the obvious one, ie treatment with sodium hydroxide. In actual practice, however, the treatment with sodium hydroxide, although usually resulting in a product having a clean odor, had several disadvantages. During the treatment with sodium hydroxide, the impure mixture of acid and fatty acid ester of sodium isethionate frequently forms into lumps in the mixing equipment. This lumping makes the operation extremely difiicult. Furthermore, there is a destruction, probably due to hydrolysis of the fatty acid esters of sodium isethionate, resulting in a loss of the desired product. In addition, the use of harsh alkalizing solutions results in corrosion to some types of equipment employed for the neutralization process. These and other difiiculties of the conventional process are overcome by the present in vention.

In has now been discovered that in a surprisingly efiicientand convenient manner the neutralization of the acidic impurities present in crude fatty acid esters of sodium isethionate is accomplished by treating the material with soap. Both water soluble and water insoluble soaps may be used, for example sodium, potassium, calcium, magnesium, aluminum, zinc, ammonium and amine soaps, formed from any of the straight or branched chain, saturated or unsaturated fatty acids normally used in soap making operations such as, for example, those having from about 10 to 22 carbon atoms, may be used, either alone or'in a mixture. It is advantageous, however, to choose 2,967,189 Patented Jan. 3, 1961 ICC the type of fatty acid salt with the ultimate use of the purified material in mind. The fatty acid esters of sodium isethionate are used commercially as detergents. A preferred method for such use involves incorporating this material into a detergent bar containing free fattyacids, e.g. stearic acid. Therefore, it is advantageous to use sodium stearate to neutralize the crude isethionate ester, since the reaction mixture will then contain stearic acid which is formed by the reaction between the sodium stearate and the acidic impurities.

Another surprising advantage of the soap method of neutralizing the isethionate esters is that there is a saving in time as compared to neutralization with caustic soda, since a shorter time is required to obtain a dry powdery state when soap is used than when caustic soda is em ployed, and it is the attainment of this powdery condition that determines when a batch may be left unattended or placed in a storage container, even though full pH equilibrium may not have been reached. I

Temperatures from about 20 C. to about 140 C. may be used, but in general, reaction is most conveniently carried out at a temperature offrom about C. to about C. The particle size of the soap to be employed is not critical, although it is generally preferred to use finely divided particles, thereby providing for easier and more thorouh mixing and for rapid reaction.

In carrying out the neutralization reaction of this invention, it is not necessary that the impure material be exactly neutralized to a pH of 7.0. Rather, it is required only that sufiicient soap be added to reduce the hydrogen ion concentration to a range of values below that associated with a strong acid solution, the preferred pH depending upon the intended use of the product. Samples of the reaction mixture may be taken preiodically and the pH thereof measured, for example in a 10% distilled water solution at 35 C. Addition of enough soap to raise the pH of the mixture to above about 4.0 is sufficient to neutralize practically all the hydrogen chloride impurity. In those cases where the isethionate ester is to be incorporated into a detergent bar containing free stearic acid, the desired final pH of the reaction mixture lies within the range of about 6 to about 10, and preferably within the range 7.3 to 7.9. It has been found con venient in practice sometimes to make the final pH adjustment, which is a very small one, with 50% sodium hydroxide. 1

Since the fatty acid ester of sodium isethionate is ultimately to be used in most case as a component in a detergent composition, it is essential that the product have a clean odor. An exceptionally clean odor is obtained when the soap contains a small proportion of free alkali, or when the neutralization is completed with a small amount of caustic alkali, as for example, about 0.6% of 50% sodium hydroxide on the total batch weight. Sodium hydroxide, when used in concentrated aqueous solution to purify the isethionate ester, sometimes does give a fairly clean odor, but other times gives a product with a bad odor. This advantage of the present invention is all the more unexpected in view of the fact that other alkaline agents, for example powdered borax, aqueous ammonium hydroxide, and powdered caustic, result in the formation of pro-ducts having poor odors. The reason for this difference in odor is not clearly understood, and this result could not possibly have been predicted.

As an alternative to the treatment of the impure fatty acid ester of sodium isethionate with soap, the process may be carried out by the formation in situ of the soap by addition of free fatty acids followed by the addition of alkali metal hydroxide. This alternative procedure also has advantages over the conventional treatment with sodium hydroxide alone, although sometimes the formation of lumps is observed during the mixing. It is re ga'rded as being 'almost as satisfactory as the direct treatment with preformed'soap.

The process of the present invention is useful for the neutralization of acidic impurities in any fatty acid ester of sodium'isethionate, but it is particularly useful in the case of the compounds most often used in the detergent industry. Thus the fatty acid esterof sodium isethionate may be one from any straight or branched chain, saturated or'uns'aturated fatty acid, particularly those having from about 10 to about 22 carbon atoms.

The following examples are given solely for purposes of illustration and are not to be considered as limiting the invention to these embodiments. Many modifications will be apparent to those skilled in the art without departing from the spirit or scope of the invention.

Example 1 1576 pounds of fatty acid esters of sodium isethionate, previously prepared by the reaction of fatty acyl chloride with sodium isethionate, were placed in a 600 gallon Sigma blade'Day mixer. The crude material contained about 1% hydrogenchloride and other acidic substances. Sodium soap, previously prepared from a mixture of about 38% palmitic acid and about 62% stearic acid and containing 8.2% water, was added in powdered form over a period of about 5 minutes with agitation. The free alkalinity of the soap was equal to 3.5% expressed as sodium hydroxide. A total of 160 pounds of the powdered soap was added. The temperature of the isethionate esters before the addition of the soap was approximately 93 C. The agitation was continued for minutes, whereupon the process was complete. The pH of the finished mixture was 7.1. 100% of the isethionate esters originally present remained after the neutralization reaction.

Example 2 ISOO'pounds of acyl (coco) isethionate were prepared infla600 gallon Sigma blade Day mixer by the reaction of'hardened coconut oil fatty acid chloride with sodium isethionate. The pH of the crude product was 2.0. One hundred and sixty pounds of sodium soap, comprising approximately 45 parts stearic and 55 parts palmitic acids, and containing an undetermined small proportion of free alkali,'was added over a period of 18 minutes and allowed to mix for a'further 35 minutes, whereupon the pH was 7.5. The temperature of the isethionate at the start of the soap addition was 79 C. (175 F.) and was 49 C. (120 'F.) at the'end of the mixing period. 100% of the isethionate esters remained after the neutralization process.

Example 3 1500 pounds of acyl (coco) isethionate were prepared in a 600 gallon Sigma blade Day mixer by the reaction of hardened coconut oil fatty acid with sodium isethionate. Fifty pounds of soap flakes prepared from a mixture of 80% tallow and 20% coconut oil (and containing no more than a trace of free alkali) was added, followed by 28 pounds of 50% caustic soda, both being added over a total period of 35 minutes. The pH of the neutralized bath was 7.1. 99.6% of the isethionate esters remained after the neutralization process.

Example 4 1400 pounds of acyl (coco) isethionate were prepared in a 600 gallon Sigma blade Day mixer by the reaction of hardened coconut oil fatty acid chloride with sodium isethionate. One hundred and fifty pounds of sodium soap (prepared from Hydrofol glycerides," a hardened tallow, having an I.V. of less than 1, and containing 6.27% water and 2.8% free alkali as NaOH) were added over'a period of 15 minutes. The pH was 7.1. 99.7% of the isethionate esters remained after the neutralization process.

Example 5 22.5 pounds of fatty acid esters of sodium isethionate were prepared in a IO-gallon Sigma blade Patterson mixer by the reaction of fatty acid acyl chloride with sodium isethionate. The crude product contained about 1% hydrogen chloride and other acidicrsubstances. The pH of a 10% aqueous solution was 3.0. After the addition of 0.87 pound of powdered coconut oil sodium soap, the pH of a 10% aqueous solution of the product was 6.9. The temperature of the isethionate esters before the soap addition was 110120 C. The product was agitated for 14 minutes after the soap addition. of the isethionate esters, originally present, remained after the neutralization reaction. (The coconut oil soap contained an undetermined small amount of free-alkali.)

Example 6 1460 pounds of fatty acid esters of sodium isethionate were prepared in a 600-gallon Sigma blade mixer by the reaction offatty acyl chloride with'sodium isethionate. The crude material (pH of 10% aqueous s'olution=23) contained about 1% hydrogen chloride and other acidic materials. 112 pounds of flaked triple pressed stearic acid were added to the agitated crude material in 14 minutes. 35 pounds of 50% sodium hydroxide were then added in 45 minutes. The temperature of the isethionate esters was about 100 C. before the addition of stearic acid. The .pH of the finished product was 6.9. 100% of the originally present isethionate esters remained after the neutralization reaction.

Example 1 7 1460 pounds of fatty acid esters of sodium isethionate were prepared in a 600-gallon Sigma blade Day mixer by the reaction of coconut fatty acid chloride with sodium isethionate. The pH of the crude product, containing about 1% hydrogen chloride and other acidic'substance's, was between 2 and 3. 136 pounds of sodium soap, pre viously prepared from a triple pressed mixture of 55% palmitic'acid and 45% stearic acid and containin'g'les's than 1% water and no free sodium hydroxide, was added in powder form overa period of -10 minutes. Thetemperature of the isethionate esters before the soap addition was approximately 100 C. Agitation was continuedfor 10 minutes to complete the process. The pH of the finished product was 6.2. 98% of the originally present isethionate esters remained after the neutralization process.

Example 8 22 pounds of fatty acid esters of sodium isethionate were prepared in a 10-gallon Sigma blade Patterson mixer by the reaction of coconut fatty acyl chloride with sodium isethionate. The crude product cantained about 1% hydrogen chloride and other acidic substances. The pH of a 10% aqueous solution was 2.7. One pound of sodium soap, previously prepared from triplepressed stearic acid, was added in powder form. The temperature of the isethionate esters was 23 C. before the soap addition. The product was agitated 15 minutes after the addition of the soap, and the final pH was 6.8. 100% of the isethionate esters originally present remained after the neutralization reaction.

Example 9 1576 pounds of fatty acid esters of sodium isethionate were prepared in a 600-gallon Sigma blade mixer by the reaction of coconut fatty acyl chloride with sodium isethionate. T-he'crude material (pH of 10% aqueous solution=23) contained about 1% hydrogen chloride and other acidic materials. 260 pounds of sodium soap (percent'H O=3.4;; percent free alkali as Na O=0.20), previously prepared from a triple pressed mixture of 55% palmitic acid and 45% stearic acid, were added-in powdered form overaperiod of 10 minutes. The tem- 'perature of the isethionate esters before the soap addition 1576 pounds of fatty acid esters of sodium isethionate were prepared in a 600-gallon Sigma blade mixer by the reaction of coconut fatty acyl chloride with sodium isethionate. To the powdered crude product was added, with mixing, 155 pounds of powdered sodium stearate (containing 95% of about a 55/45 mixture of palmitate and stearate, less than 1% free alkali as NaOH, and the balance water) over a period of 3 minutes. The temperature of the isethionate esters before the soap addition was approximately 190 F. Ten pounds of 50% caustic soda solution was then added over a period of 5 minutes, and the agitation was continued for a further 5 minutes. The batch remained in a powdery condition. The pH of the finished product was 7.3. The color and odor were good. 100% of the originally present isethionate esters remained after the process.

Example 11 22.5 pounds of fatty acid esters of sodium isethionate were prepared in a gallon Sigma blade Patterson mixer by the reaction of fatty acid acyl chloride with sodium isethionate. The crude product contained about 1% hydrogen chloride and other acidic substances. The pH of a 5% aqueous solution was 2.2. After the addition of 2.2 pounds of powdered calcium stearate, the pH of a 5% aqueous solution of the product was 6.7. The temperature of the isethionate esters before the calcium soap addition was 101 C. The product was agitated for 23 minutes after the calcium soap addition. 100% of the isethionate esters, originally present, remained after the purification reaction.

Example 12 22.6 pounds of fatty acid esters of sodium isethionate were prepared in a 10 gallon Sigma blade Patterson mixer by the reaction of fatty acid acyl chloride with sodium isethionate. The crude product contained about 1% hydrogen chloride and other acidic substances. The pH of a 5% aqueous solution was 2.1. After the addition of 2.2 pounds of powdered magnesium stearate, the pH of a 5% aqueous solution of the product was 6.9. The temperature of the isethionate esters before the magnesium soap addition was 95 C. The product was agitated for 30 minutes after the magnesium soap addition. 100% of the isethionate esters, originally present, remained after the purification reaction.

Example 13 22.57 pounds of fatty acid esters of sodium isethionate were prepared in a 10 gallon Sigma blade mixer by the reaction of coconut fatty acid acyl chloride with sodium isethionate. The crude product contained about 1% hydrogen chloride and other acidic impurities. The pH of a 5% aqueous solution was 2.5. After the addition of 2.2 pounds of powdered potassium coconut oil soap, the pH of a 5% aqueous solution of the product was 7.25. The temperature of the isethionate esters was 82 C. before addition of the soap. The product was agitated for 25 minutes after the soap addition. 100% of the isethionate esters, originally present, remained after the neutralization reaction.

Example 14 22.50 pounds of fatty acid esters of sodium isethionate were prepared in a 10 gallon Sigma blade mixer by the mained after the neutralization of the acidic impurities.

Example 15 22.50 pounds of fatty acid esters of sodium isethionate were prepared in a 10 gallon Sigma blade mixer by the reaction of fatty acid coconut acyl chloride with sodium isethionate. The crude product contained about 1% hydrogen chloride and other acidic impurities. of a 5% aqueous solution was 2.3. After addition of 2.2 pounds of powdered aluminum stearate, the pH of a 5% aqueous solution of the product was 4.5. The temperature of the isethionate esters before the addition of aluminum stearate was C. The product was agitated for 20 minutes after the addition of the aluminum soap. of the isethionate esters, originally present, remained after the neutralization.

Example 16 22.5 pounds of fatty acid esters of sodium isethionate were prepared in a 10 gallon Sigma blade mixer by the reaction of coconut fatty acid acyl chloride with sodium isethionate. The product contained about 1% hydrogen chloride and other acidic impurities. The pH of a 5% aqueous solution was 2.4. After the addition of 2.2 pounds of powdered zinc stearate, the pH of a 5% aqueous solution of the product was 5.0. The temperature of the isethionate esters before the addition of zinc stearate was 70 C. The product was agitated for 20 minutes after the soap addition. 100% of the isethionate esters, originally present, remained after the neutralization reaction.

Example 17 20.5 pounds of fatty acid esters of sodium isethionate Were prepared in a 10 gallon Sigma blade mixer by the reaction of coconut fatty acid acyl chloride with sodium lsethionate. The product contained about 1% hydrogen chloride and other acidic impurities. The pH of a 5% aqueous solution was 2.8. After the addition of 1.8 pounds of powdered magnesium laurate, the pH of a 5% aqueous solution of the product was 6.8. The temperature of the isethionate esters before the addition of magnesium laurate was 40 C. The product was agitated for 35 minutes after the magnesium soap addition. 100% of the isethionate esters, originally present, remained after the neutralization reaction.

Example 18 22.4 pounds of fatty acid esters of sodium isethionate were prepared in a 10 gallon Sigma blade mixer by the reaction of coconut fatty acid acyl chloride with sodium isethionate. The product contained about 1% hydrogen chloride and other acidic impurities. The pH of a 5% aqueous solution was 2.5. After the addition of 4 pounds of ammonium stearate, the pH of a 5% aqueous solution of the product was 6.3. The temperature of the isethionate esters before the addition of the ammonium stearate was 48 C. 100% of the isethionate esters, originally present, remained after the neutralization reactlon.

The .pHv

7 Example 19 22.5 .pounds of fatty acid esters of sodium isethionate were prepared in a 10 gallon Sigma blade Patterson mixer by the reaction ofcoconut fatty acid acyl chloride with sodium isethionate. The crude product contained about 1% hydrogenchloride and other acidic substances. .The .pH of a 5% aqueous solution was 2.2. After the addition of 2.2 pounds of powdered calcium stearate the pH of a 5% aqueous solution of the product was 6.7. The temperature of the isethionate esters before the calcium soap addition was 101 C. The product was agitated for 23 minutes after the calcium soap addition. 100% of the isethionate esters, originally present, remained after the purification reaction.

Example 20 22.6 pounds of coconut fatty acid esters of sodium isethionate were prepared in a gallon Sigma blade Patterson mixer by the reaction of fatty acid acyl chloride with sodium isethionate. The crude product contained about 1% hydrogen chloride and other acidic substances. The pH of a 5% aqueous solution was 2.1. After the addition of 2.2 pounds of powdered magnesium stearate, the pH of a 5% aqueous solution of the product was 6.9. The temperature of the isethionate esters before the magnesium soap addition was 95 C. The product was agitated for 30 minutes after the magnesium soap addition. 100% of the isethionate esters, originally present, remained after the purification reaction.

What is claimed is:

1. A process for the neutralization of acidic impurities in a fatty acid ester of sodium isethionate, said process comprising treating the impure fatty acid ester of sodium isethionate with a soap. i

2. A process as claimed in claim 1 wherein the temperature of the reaction is between about 20 C. and 140 C.

3. A process as claimed in claim 1 wherein the soap is mixed in the powdered form With the impure fatty acid ester of sodium isethionate.

4. A process for the neutralization of acidic impurities in a fatty acid ester of sodium isethionate, said process comprising treating the impure fatty acid ester of sodium isethionate with an alkali metal soap formed in the reaction mixture by the reaction of free fatty acid and alkali hydroxide.

5. A process as claimed in claim 1 wherein the final reaction mixture has a pH between about 4.0 and about 10.0.

6. A process .as claimed in claim 1 wherein a ,small amount of caustic soda is also employed as a neutraliz ing agent.

7. A process for the neutralization of acidic impurities in a fatty acid ester of sodium isethionate, said process comprising treating the impure fatty acid ester of sodium isethionate with the sodium salt of stearic acid.

8. A process for the neutralization of acidic impurities in a fatty acid ester of sodium isethionate, said process comprising reacting at a temperature between C. and C. the impure fatty acid ester of sodium isethionate with sodium stearate to produce a reaction mixture having a pH between 7.3 and 7.9.

No. references cited. 

1. A PROCESS FOR THE NEUTRALIZATION OF ACIIDIC IMPURITIES IN A FATTY ACID ESTER OF SODIUM ISETHIONATE, SAID PROCESS COMPRISING TREATING THE IMPURE FATTY ACID ESTER OF SODIUM ISETHIONATE WITH A SOAP. 